Introduction

Assembly Spy is a very nice simple application written in VB.NET that uses reflection to dynamically inspect assemblies and list the containing types and members of the selected type.

The following figure shows application’s only window loading .NET 2.0 mscorlib.dll and lists members of System.String.

Background

Here are some things that should be kept in your mind:

All types (classes, structures, enumerations, etc.) inherit -directly or indirectly- from System.Type, and System.Type, in turn, inherits from System.Object. Therefore, System.Type can represent any other type.

Reflection, as described in MSDN, is a CLR feature allows you to obtain information about assemblies and types defined within them dynamically (on the fly.)

All types related to reflection are grouped together inside the namespace System.Reflection in the core COR (Common Object Runtime) assembly, mscorlib.dll.

Reflection represents type members as objects inherit from System.Reflection.MemberInfo class. We will see how soon.

Visual Studio’s Object Browser and Class Viewer (WinCV) are the most illustrative examples of tools that use reflection to obtain information about types in a given assembly.

Sample Code

It allows you to select an assembly, and it lists types defined within that assembly it in the left pane. When you select a type, it automatically lists type members in the right pane of the window.

After loading the assembly using the shared method System.Reflection.LoadFrom(), the application retrieves an array of all types defined inside this assembly (accurately, module) and calls our core function ListModuleTypes() to list the types into the List Box:

Private Sub ListModuleTypes(ByRef tTypes() As System.Type)
Dim tType As System.Type
For Each tType In tTypes
If (tType.IsPublic) Then
lbNamespaces.Items.Add(tType.FullName)
End If
Next
End Sub

When a user selects a type, the code clears out members tree view and adds the members of the newly selected type. Those members are categorized into those categories:

Every one of our System.Type.GetXXX() functions returns an array of types inherit from System.Reflection.MemberInfo class. This allows us to polymorphically enumerate the array and work with all class members the same way. The following illustration should give you a basic understanding of how types are related to each other.

The code uses the following function add members to the members tree view:

Private Sub ListMembers(ByVal miElements() As System.Reflection.MemberInfo)
Dim miElement As System.Reflection.MemberInfo
For Each miElement In miElements
tnNode = New TreeNode
tnNode.Text = System.Convert.ToString(miElement)
tvMembers.SelectedNode.Nodes.Add(tnNode)
Next
End Sub

Download

Code sample and application are attached with the article. The setup file installs both the application and its source code.

I created this application since several years ago when I was discovering .NET for the first time. Honestly, the UI of this sample originated from a VB.NET book. I really know neither the name of that book nor the name of its author. However, a big €œThank You€ to the author and the book.